1. Field of the Invention
The present invention relates to an improvement in the rechargeable batteries in which chemical reaction with lithium is utilized (these rechargeable batteries will be hereinafter collectively referred to as rechargeable lithium battery) and also in the rechargeable zinc series batteries. More particularly, the present invention relates to improved rechargeable lithium batteries and improved rechargeable zinc series batteries which effectively prevent a dendrite (or a branched tree-like protrusion) of lithium or zinc from growing upon repetition of charging and discharging, always exhibit an excellent current collecting performance over a long period of time, and has a prolonged cycle life (that is, a prolonged charging and discharging cycle life).
2. Related Background Art
In recent years, heating of the earth because of the so-called greenhouse effect due to an increase of atmospheric CO2 has been predicted.
In the case of the steam-power generation, the amount of a fossil fuel represented by coal or petroleum to be consumed for power generation in order to comply with a societal demand for increased power supply has been continuously increased and along with this, the amount of exhaust fumes from the steam-power generation plants has been continuously increased accordingly to raise the content of gases to cause a greenhouse effect such as carbon dioxide gas in the air. This results in providing an earth-warming phenomenon. In order to prevent said earth-warming phenomenon from further developing, there is a tendency of prohibiting to newly establish a steam-power generation plant in some countries.
Under this circumstance, there have been made a proposal of conducting so-called load leveling in order to effectively utilize the power generator, wherein rechargeable batteries are installed at general houses and a surplus power unused in the night, that is, a so-called dump power, is stored in said rechargeable batteries and the power thus stored is supplied in the daytime when the power demand is increased, whereby the power generator is leveled in terms of the load therefor.
By the way, there is an increased societal demand for developing a lightweight rechargeable battery with a high energy density for an electric vehicle which does not exhaust any air polluting substance such as COx, NOx, SOx, hydrocarbon, and the like. Other than this demand, there are another increased societal demand for developing a miniature, lightweight, high performance rechargeable battery usable as a power source for potable instruments such as small personal computers, word processors, video cameras, and pocket telephones.
As such rechargeable battery, there has been proposed a rocking chair type lithium ion cell in which a lithium intercalation compound is used as an anode active material and carbon is used as a cathode active material. However, as of the present time, there has not realized a practically usable lithium ion battery having a sufficiently high energy density, which is considered could be attained by using a metallic lithium as the anode active material.
The public attention has now focused on the rechargeable lithium battery in which metallic lithium is used as an anode, but as of the present time, there has not yet attained a practically usable, high capacity rechargeable lithium battery with an improved energy density. Particularly, as for the known rechargeable lithium battery, there is a problem in that lithium is often deposited in a dendritic state (that is, in the form of a dendrite) on the negative electrode during charging operation, wherein such deposition of lithium in a dendritic state results in causing internal shorts or self-discharge. As one of the reasons why such practically usable, high capacity rechargeable lithium battery as above described has not yet realized, there is a fact that a manner capable of preventing the occurrence of the above dendritic lithium deposition has not developed.
Now, as above described, when the above lithium dendrite should be once formed, the dendrite is liable to gradually grow upon charging, resulting in causing internal shorts between the anode and the cathode. When the anode is internally shorted with the cathode as above described, the energy possessed by the battery is shortly consumed at the internally shorted portion to entail problems such that the battery is heated or the solvent of the electrolyte is decomposed by virtue of heat to generate gas, resulting in raising the inner pressure of the battery. These problems result in damaging the rechargeable battery or/and shortening the lifetime of the battery.
There has been proposed a manner of using a lithium alloy such as lithium-aluminum alloy as the anode for a rechargeable lithium battery in order to suppress the reactivity of the lithium so that a lithium dendrite is hardly generated. This manner is effective in preventing the generation of the lithium dendrite but is not effective in attaining a rechargeable lithium battery having a high energy density and which is long enough in cycle life.
Particularly, Japanese Unexamined Patent Publication No. 13264/1988 (hereinafter referred to as document 1), No. 47381/1993 (hereinafter referred to as document 2) or No. 190171/1993 (hereinafter referred to as document 3) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a lithium alloy.
Additionally, Japanese Unexamined Patent Publication No. 114057/1988 (hereinafter referred to as document 4) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a basic constituent comprising a sintered body of a mixture composed of fibrous aluminum and fibrous metal incapable of being alloyed with lithium and a negative material comprising a lithium-aluminum alloy.
Further, Japanese Unexamined Patent Publication No. 234585/1993 (hereinafter referred to as document 5) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a member made of lithium metal, having powdery metal (which hardly forms an intermetallic compound with said lithium metal) uniformly deposited on the surface thereof.
Further in addition, Journal of Applied Electrochemistry, 22, 620-627 (1992) (hereinafter referred to as document 6) discloses a rechargeable lithium battery in which the anode is constituted by an aluminum foil having a surface applied with etching treatment.
However, any of the rechargeable batteries disclosed in the documents 1 to 6 is still problematic in that when the charging and discharging cycle is repeated at a practical level, the growth of a dendrite is often occurred to deteriorate the battery performance.
In order to eliminate this problem, there can be considered a manner wherein the anode and cathode are arranged such that they are closely opposed to each other through the separator. However, this manner is not effective in solving the problem because there is a tendency for the charging and discharging cycle life to be remarkably shortened to such an extent that is shorter than that in the case where the anode comprised of carbon is used.
Such problem occurred in the foregoing rechargeable batteries is liable to occur also in the conventional rechargeable nickel-zinc batteries, rechargeable zinc-oxygen (or zinc-air) batteries and rechargeable bromine-zinc batteries, in that in any of these batteries, when the anode and cathode are arranged such that they are closely opposed to each other through the separator, the charging and discharging cycle life is liable to remarkably shorten.
Accordingly, there is an increased demand for provision of an improved, highly reliable secondary cell which is high in energy density (or charge energy density) and long enough in charging and discharging cycle life.
A principal object of the present invention is to eliminate the foregoing problems found in the known rechargeable batteries and to provide an improved rechargeable which is free of such problems.
Another object of the present invention is to provide a highly reliable rechargeable which is high in energy density and long enough in cycle life (that is, charging and discharging cycle).
A further object of the present invention is to provide a rechargeable battery having an improved anode structured which is free of growth of a dendrite even when the charging and discharging are alternately repeated over a long period of time, and it makes the rechargeable battery to stably exhibit an excellent current collecting performance without being deteriorated.
A further object of the present invention is to provide a highly reliable rechargeable battery having a simple structure which can be easily handled and which can be efficiently produced by the conventional technique.
A further object of the present invention is to provide a highly reliable rechargeable battery which can be mass-produced without a variation in terms of the battery performance.
A further object of the present invention is to provide a highly reliable rechargeable battery comprising an anode (or a negative electrode), a separator, a cathode (or a positive electrode), an electrolyte or an electrolyte solution, and a housing, characterized in that said anode is structured to have a size which is larger than that of said cathode, said rechargeable battery being high in energy density and having a prolonged cycle life.
A further object of the present invention is to provide a rechargeable battery comprising an anode, a separator, a cathode, an electrolyte or an electrolyte solution, and a housing, characterized in that said anode or/and said cathode have an edge portion covered by an insulating material or semiconductor material, said rechargeable battery being high in energy density and having a prolonged cycle life.
The term xe2x80x9crechargeable batteryxe2x80x9d in the present invention includes a rechargeable lithium battery, a rechargeable nickel-zinc battery, a rechargeable zinc-oxygen battery, and a rechargeable bromine-zinc battery.